The long range goal of the program is to develop gene therapy for Gaucher disease (GD), the most common lysosomal storage disorder and the most prevalent Jewish genetic disease. The unique pathobiology of the disease makes it an excellent candidate for a gene transfer approach to its therapy. Macrophages are a primary target of the proposed gene transfer studies because they are the cells most affected by the accumulation of glucosylceramide. They are central to the pathogenesis of GD and, in type 1 disease, are the only cells that store the glycolipid. Furthermore, both bone marrow transplantation (BMT) and correction of macrophage enzymatic activity by enzyme replacement are therapeutic. In the current proposal, model systems will be used to evaluate the possibility of gene transfer as a means to correct the deficiency of glucocerebrosidase (GC) in hematopoietic cells. In preliminary studies, we used a retroviral vector (MFG-GC) to transfer the GC gene. The vector was tested in a murine model of BMT and shown to efficiently transfer the gene and resulted in sustained expression of the GC gene in hematopoietic stem cells and their progeny including macrophages and secondary CFU-S for up to 7 months in vivo. These results permit extension of these studies to dog and human hematopoietic cells including CD 34+ cells from bone marrow and peripheral blood and macrophage precursors or stem cells derived from long-term bone marrow cultures (LTBMC). The evaluation of gene transfer to human cells will include the ability of the vector to correct GC deficiency in potentially transplantable human cells from GD patients. Study of the ability of human hematopoietic cells to sustain expression of the transferred GC gene in vivo will be studied by transplantation of human cells to the severe combined immunodeficient mouse model (SCID). In a transgenic mouse model of GD, the vector will be used to determine the number and survival of transduced cells, duration and strength of GC expression, percentage correction of deficient GC activity needed to be effective, and potential adverse actions. Taken together, these studies should provide a basis for the evaluation of the potential of gene therapy as a treatment for Gaucher disease.